Assessing the Capability and Potential of LiDAR for Weed Detection

Conventional methods of uniformly spraying fields to combat weeds, requires large herbicide inputs at significant cost with impacts on the environment. More focused weed control methods such as site-specific weed management (SSWM) have become popular but require methods to identify weed locations. Advances in technology allows the potential for automated methods such as drone, but also ground-based sensors for detecting and mapping weeds. In this study, the capability of Light Detection and Ranging (LiDAR) sensors were assessed to detect and locate weeds. For this purpose, two trials were performed using artificial targets (representing weeds) at different heights and diameter to understand the detection limits of a LiDAR. The results showed the detectability of the target at different scanning distances from the LiDAR was directly influenced by the size of the target and its orientation toward the LiDAR. A third trial was performed in a wheat plot where the LiDAR was used to scan different weed species at various heights above the crop canopy, to verify the capacity of the stationary LiDAR to detect weeds in a field situation. The results showed that 100% of weeds in the wheat plot were detected by the LiDAR, based on their height differences with the crop canopy.

SENSITIVITY ANALYSIS OF AQUACROP EVAPOTRANSPIRATION TO WEATHER STATION DISTANCE

Water balance calculation is essential for reliable agricultural management, and theactual evapotranspiration (ET) is the most complicated balance term to estimate. Inagriculture, the most common method used is based on Penman-Monteith referenceevaporation is determined from weather conditions for an unstressed grass cover,further multiplied by crop specific and soil water availability coefficients to obtainthe actual evapotranspiration. This approach is also used in the AquaCrop model.This model has proven to be accurate when all weather data are locally available.However, in many cases, weather data can’t be collected on the site due to thelimited number of stations and the vast region covered by each of them. Instead,data are often collected at many kilometers from the study site. The question wewant to study is: how does evapotranspiration accuracy evolves with respect toweather station distance? A winter wheat plot in Lonzée (Belgium) was studiedduring the 2014-2015 agricultural seasons. Actual evapotranspiration wassimulated with AquaCrop thanks to the weather data collected at 3 differentdistances from the study site: on the site (data collected by a fluxnet station), 20km, 50 km and 70km from the site. The non-on-site weather data were derivedfrom spatially interpolated 10 km grid data. These results were then compared tothe fluxnet station evapotranspiration measurements to assess the impact of theweather station distance. Substantial differences, which were found between thefour cases, evoking the importance of assimilating satellite derived ET products(e.g. MSG) into AquaCrop.

EFFECT OF LONG-TERM CONTINUOUS CROPPING OF SPRING WHEAT ON AGGRESSIVENESS OF Cochliobolus sativus

Cochliobolus sativus cultures were collected from symptomatic wheat plants from a plot planted continuously to wheat for over 90 yr and from symptomatic wheat plants in commercial grain fields cropped rotationally in the surrounding area. Pathogenicity of these isolates was tested in replicated greenhouse trials using wheat plants scored for disease 6 wk after inoculation. Isolates from the continuous-cropped wheat plot were more aggressive on average than were isolates from commercial fields. Long-term continuous cropping to wheat appears to shift the population of C. sativus toward more aggressive types, although many less aggressive types also remain.Key words: Aggressiveness, Drechslera sorkiniana, Helminthosporium sativum, wheat root rot

EFFECT OF DIFFERENT PLOT BORDERS ON GRAIN YIELDS IN BARLEY AND WHEAT

Ten genotypes of barley (Hordeum vulgare L.) and 10 genotypes of wheat (Triticum aestivum L.) were grown with four types of plot borders (control, same genotype as the plot; unbordered; winter wheat; spring barley/wheat) to study the influence of plot borders on the ranking for yield of cereal genotypes. Plot yields increased as border competition decreased. However, the ranking of the different genotypes was not influenced by the type of plot border, except when a highly competitive barley genotype was used as a border with wheat. It was concluded that the type of plot border was of relatively little importance in selection for yield, as long as the border was not more competitive than the plot.Key words: Barley, wheat, plot borders, yield, plant competition, varietal ranking

VARIATION IN NUMBERS OF BACTERIA IN TWO PLOTS

An experiment was designed to study the combined effect of changes in moisture, dates of sampling, and numbers of colonies per plate on the estimated number of bacteria in the soil of two plots. The data represent 30 replicate estimates on a wheat plot and 30 on a fallow plot, each made from a different dilution on each of 19 dates of sampling from May 21 to September 27, together with moisture determinations for each plot on each date. The statistical treatment consists of a combination of correlation and analysis of variance studies. The results are presented graphically, and in the usual form of analysis of variance. They demonstrate the presence of a basic population in each plot which responds differently to moisture and time in different dilutions.